Phthalocyanine analogs

ABSTRACT

Disclosed are compounds of formula V                    
     wherein M is selected from: a metal atom; a metal compound; 2H whereby one H is bonded to each of the two nitrogen atoms depicted as being bonded to M (positions 29 and 31 shown) R 3  is H or methyl; R 1  and R 4  are independently selected from: H, C 1  to C 4  alkyl, C 2  to C 4  alkenyl, methoxy, butoxy, propoxy, NH 2 , NH—(C 1  to C 4  alkyl), N—(C 1  to C 4  alkyl) 2 , S—(C 1  to C 4  alkyl); R 8  to R 25  are the same or different and are independently selected from: C 1  to C 32  alkyl; C 2  to C 32  alkenyl; X—O—Y; X—phenyl, X 2 COOX 1 , X 2 CONR 1 R 11 , H; halide; wherein: X and X 2  are independently selected from: a chemical bond, —(CH 2 ) n — wherein n is an integer from 1 to 32, —(CH 2 ) a —CH═CH(CH 2 ) b  where a and b are independently selected from integers 0-32 and a+b totals 32; X 1  and Y are independently selected from: C 1  to C 32  alkyl, C 2  to C 32  alkenyl, and H; R 1  and R 11  are independently selected from: H; C 1  to C 32  alkyl, C 2  to C 32  alkenyl, —(CH 2 ) n —; with the proviso that at least one of R 8  to R 25  is selected from: C 1  to C 32  alkyl, C 2  to C 32  alkenyl, X—O—Y, X—phenyl, X 2 COOX 1 , X 2 CONR 1  R 11 .

The present invention relates to phthalocyanine analogs, in particularlyto azaphthalocyanines (pyridinoporphyrazines). It further relates tocompositions containing these compounds, and methods of use of suchcompounds and compositions.

Phthalocyanine is shown in FIG. 1 (a). The nomenclature for thenumbering of the Benzo portion is also included in the above depiction.Generally substituents in the R2, 3, 9, 10, 16, 17, 23, 24 positions arereferred to as peripheral groups and substituents in the R1, 4, 8, 11,15, 18, 22, 25 positions are referred to as non-peripheral groups.

Often, phthalocyanine is abbreviated to Pc.

Pcs in condensed phases possess interesting optical absorptionsignatures. semiconductivity and optoelectronic properties which areoften sensitive to molecular packing. Normally, the planar molecules areprone to form co-facial or near co-facial assemblies. These“Face-to-Face” structures include the simple aggregates found insolution,² the longer columnar stacks in the liquid crystal phases ofmesogenic derivatives,³ and the classic “herring bone” columnar packingin the most common polymorphs of the unsubstituted compounds.⁴ Polymericcolumnar structures include the “shish-kebab” polymers formed when thecentral metal atoms of neighbouring Pc units are covalently orcoordinatively linked via bridging atoms or molecules.⁵

The unusual properties that Pcs and Pc analogs exhibit means they havemany applications.

UK Patent GB 2,229,190 B relates to certain novel substitutedphthalocyanines, methods for their preparation and to certain usesthereof. For example the compounds described in GB 2,229,190 B aresuitable for use in optical recording media. Kuder in J. of ImagingScience, vol. 32, (1988), pp51-56 discusses how phthalocyanine dyes maybe used in laser addressed optical recording media; in particular itsets out how active layers may be deposited.

UK Patent Application 9317881.2 describes substitutedmetallophthalocyanines and phthalocyanines as PDT agents.

Patent application WO 93/09124 describes the use of water soluble saltor acid forms of transition metal phthalocyanines for use inphotodynamic therapy. In this patent application, phthalocyaninescontaining second or third row transition metals with a d6 low-spinelectronic configuration are disclosed. The compounds exemplified inpatent application WO 93/09124 contain Ru.

Phthalocyanine derivatives have also been used in Langmuir Blodgettfilms as described in UK Patent 2,229,190 B.

The redox behaviour of phthalocyanines is also of interest. Some useswhich exploit the redox properties of phthalocyanines includeelectrocatalysis, photocatalysis, photovoltaics, electric conduction,photoconductivity and electrochromism. These uses (amongst others) ofphthalocyanines are discussed by A. B. P. Lever in Chemtech, 17,pp506-510, 1987.

Certain pyridinoporphrazines (azaphthalocyanines, or AzaPcs)have beenprepared and reported in the literature. These include tetrapyridinoderivatives and bipyridino derivatives having Cr, Co, Cu, Fe and Nicentres. Thus Linstead⁷ first demonstrated the replacement of all fourbenzene rings of the Pc nucleus by pyridine in his classicinvestigations in the 1930s, obtaining a mixture of insoluble isomericdyes from 3,4-dicyanopyridine. Subsequently, Shibamiya and coworkersprepared unsubstituted macrocycles containing combinations of bothbenzenoid and pyridinoid rings.⁸ The absorption spectra of thesecompounds were described, although not with reference to any particularapplications.

It can thus be seen that the provision of novel Pc derivatives (or usesfor such derivatives) particularly those with novel absorptionsignatures, would provide a contribution to the art.

DISCLOSURE OF THE INVENTION

The present inventors have now produced and characterised novel organicsolvent-soluble AzaPcs in which a pyridinoid ring is incorporated in oraround the Pc nucleus. Such compounds provide, inter alia, for thegeneration of “Edge-to-Face” assemblies via metal-nitrogen coordinationinvolving the pyridyl nitrogen atom of one molecule and the metal ion ofa second molecule.

Although Edge-to-Face assembles have been constructed earlier usingporphyrin derivatives,⁶ they have not as yet been realised within the Pcseries. Such compounds have unexpected and industrially applicableproperties in a variety of technical fields as is described in furtherdetail hereinafter.

Thus according to one aspect of the invention there is disclosed anAzaPc of Formula I (FIG. 1(b)):

wherein:

M is selected from:

a metal atom; a metal compound; 2H whereby one H is bonded to each ofthe two nitrogen atoms depicted as being bonded to M (positions 29 and31 shown)

and wherein:

one or more of the Q groups is selected from: formula II or formula III,with the remaining Q groups each being formula IV:

wherein:

R₃₃ and R₃₄ are independently selected from: H or methyl

R₃₅ is selected from: H; C₁ to C₄ alkyl; C₂ to C₄ alkenyl; methoxy;butoxy; propoxy; NH₂; NH—(C₁ to C₄ alkyl); N—(C₁ to C₄ alkyl)₂, S—(C₁ toC₄ alkyl).

each R_(n) and R_(p) group is independently selected from: C₁ to C₃₂alkyl; C₂ to C₃₂ alkenyl; X—O—Y; X—phenyl X²COOX¹; X²CONR¹R¹¹; H; halide

wherein:

X and X² are independently selected from: a chemical bond; —(CH₂)_(n)—wherein n is an integer from 1 to 32; —(CH₂)_(a)—CH═CH(CH₂)_(b) where aand b are independently selected from integers 0-32 and a+b totals 32.

X¹ and Y are independently selected from: C₁ to C₃₂ alkyl; C₂ to C₃₂alkenyl; H

R¹ and R¹¹ are independently selected from: H; C₁ to C₃₂ alkyl; C₂ toC₃₂ alkenyl; —(CH₂)_(n)—

with the proviso that where more than one Q is Formula II with theremaining Q group being Formula IV, at least one of the R₃₃, R₃₄, R₃₅,R_(n), or R_(p) groups is not H.

In a further, preferred aspect of the invention, there is disclosed anAzaPc having formula V (FIG. 1(f)).

Wherein:

M is selected from:

a metal atom; a metal compound; 2H whereby one H is bonded to each ofthe two nitrogen atoms depicted as being bonded to M (positions 29 and31 shown)

R₃ is H or methyl

R₁ and R₄ are independently selected from: H; C₁ to C₄ alkyl; C₂ to C₄alkenyl; methoxy; butoxy; propoxy; NH₂; NH—(C₁ to C₄ alkyl); N—(C₁ to C₄alkyl)₂, S—(C₁ to C₄ alkyl).

R₈ to R₂₅ are the same or different and are independently selected from:

C₁ to C₃₂ alkyl; C₂ to C₃₂ alkenyl; X—O—Y; X—phenyl

X²COOX¹; X²CONR¹R¹¹; H; halide

wherein:

X and X² are independently selected from: a chemical bond: —(CH₂)_(n)—wherein n is an integer from 1 to 32; —(CH₂)_(a)—CH═CH(CH₂)_(b) where aand b are independently selected from integers 0-32 and a+b totals 32.

X¹ and Y are independently selected from: C₁ to C₃₂ alkyl; C₂ to C₃₂alkenyl; H

R¹ and R¹¹ are independently selected from: H; C₁ to C₃₂ alkyl; C₂ toC₃₂ alkenyl; —(CH₂)_(n)—

Most preferably the compound has formula VI (as shown in FIG. 1(g),wherein M=2H, Ni, Zn, Co, Cu, Pd, Ru or Al.

Referring to formula I, formula VI has one Q group of formula II withthe remaining Q groups each being formula IV. R₃₃, R₃₄ and R₃₅ are H;R_(n) are C₈ alkyl and R_(p) is H.

Preferred Compounds

Preferred compounds of the present invention are those wherein any oneor more of the following apply:

All non-peripheral R groups (e.g. R_(n) in formula III and IV) are H.

All R groups other than those attached to pyridyl nuclei are alkylcontaining up to 32 (preferably up to 20, more preferably between 4-14or between 8-12) C atoms where 1 or more adjacent CH₂ groups may bereplaced by O or a double bond, and the remaining R groups are all H.

All peripheral R groups other than those attached to pyridyl nuclei arealkyl containing up to 32 (preferably up to 20, more preferably between4-14 or between 8-12) C atoms, and the remaining R groups are all H.

The R groups attached to the or each pyridyl nucleus on the C atomsadjacent the N (i.e. R₃₃,R₃₄,R₁,R₃ as appropriate) are H, therebyminimising steric hindrance in those embodiments of the invention whichform “edge-to-face” dimers or higher oligomers.

The R group attached to the or each pyridyl nucleus which is in themeta-position with respect to the N (i.e. R₃₅ or R₄ as appropriate) isan electron donating group thereby increasing the basicity of the N suchas to enhance its properties as a ligand.

Examples of this type of group include O-alkyl. NH₂, NH-alkyl,N(alkyl)₂, alkyl, S-alkyl.

In all cases the alkyl groups may be straight or branched chain.Straight chain are preferred.

The compounds of the invention may be metal free or contain a metalbound to a ligand (such compounds may have utility, inter alia, in themanufacture of metal containing derivatives, for instance asintermediates) or may contain a metal atom, preferably a diamagneticmetal atom.

The metal atom may be present for example as the metal with an oxidationstate of +2 or it may be present with other ligands (or anions) attachedto it. These ligands (or anions) may serve the purpose of altering thehydrophobicity of the molecule as a whole. Examples of suitable anionsinclude chloride, bromide or oxide. Examples of suitable metals includeRu, Ni, Pb, V, Pd. Co, Nb, Al, Sn, Zn, Cu, Mg, Ca, In, Ga, Fe, Eu, Luand Ge. Preferably when M is a metal or metal compound then the metalis, or the metal compound contains Cu, Zn, Ru, Pb, V, Co, Eu, Lu, Al.Examples of suitable metal compounds include VO and TiO. Those which maypreferentially form “edge-to-face” dimers or higher oligomers underappropriate conditions include Zn, Cu, Co, Ru, and Ni.

Applications

Methods of use of the compounds described above form further aspects ofthe present invention. Some particular applications are exemplifiedbelow:

PDT

In this application it is preferred that M in the compounds of thepresent invention is diamagnetic e.g. a second or third row transitionmetal with a d⁶ low-spin electronic configuration, preferably Zn.Ru-containing compounds may also be advantageous.

A number of Pc derivatives have previously been proposed as potentialphotodynamic therapeutic (PDT) agents. The combination of a sensitizerand electromagnetic radiation for the treatment of cancer is commonlyknown as photodynamic therapy. In the photodynamic therapy of cancer,dye compounds are administered to a tumour-bearing subject. These dyesubstances may be taken up, to a certain extent, by the tumour. Uponselective irradiation with an appropriate light source the tumour tissueis destroyed via the dye mediated photo-generation of species such assinglet oxygen or other cytotoxic species such as free radicals, forexample hydroxy or superoxide. Most biological studies on Pc compoundsrelated to PDT have been conducted with water soluble sulfonatedmetallo-phthalocyanines as described by I. Rosenthal, Photochem.Photobiol. 53(6), 859-870, 1991. Methods for synthesizing thesecompounds often results in mixtures of compounds containing a variety ofisomers and/or different degrees of sulfonation.

Ideally compounds for use as photosensitizers in PDT have some or all ofthe following characteristics: solubility; high quantum yield ofreactive species; low toxicity; high absorption coefficients, preferablyin the red or near infra red of the spectrum; selective accumulation inthe tumour.

The reason why absorption in the red-region of the EM spectrum isdesirable is that red light shows greater penetration than light ofshorter wavelengths. Such sensitisers can be irradiated e.g. with laserlight, or from other non-laser sources e.g. tungsten halogen light.

The compounds of the present invention are particularly advantageous inthis regard because of their spectral properties, their ability to formhigh concentrations of dimers which fluoresce, and their solubility.Preferred compounds have Zn ,Ru or Al as their metal centre, since thesehave previously been shown (in other PCs) to be effective generators ofsinglet oxygen.

One aspect of the present invention provides a pharmaceuticalcomposition comprising a compound of the invention (e.g Formula VIwherein M is Zn or Ru) in a mixture or in association with apharmaceutically acceptable carrier or diluent.

Also embraced is use of such a compound in the preparation of amedicament, preferably a medicament for treatment against cancer, mostpreferably for the treatment of a mammal having a tumour susceptible tophotodynamic treatment.

In a further aspect, the invention also includes a method of treatmentof a mammal having a tumour susceptible to photodynamic treatment,wherein the mammal is administered an effective dose of a compound offormula I or a pharmaceutically acceptable salt form thereof and thetumour is subjected to suitable electromagnetic radiation.

The compounds described by the present invention may be induced to actas a photosensitizers by incident electromagnetic radiation of asuitable wavelength. Preferably, the electromagnetic radiation issomewhere in the range ultra-violet to infra-red, even more preferablyit is in the range visible to red to near infra-red.

The pharmaceutical compositions may be formulated according towell-known principles and may desirably be in the form of unit dosagesdetermined in accordance with conventional pharmacological methods. Theunit dosage forms may provide daily dosage of active compound in asingle dose or in a number of smaller doses. Dosage ranges may beestablished using conventional pharmacological methods and are expectedto lie in the range 1 to 60 mg/kg of body weight. Other active compoundsmay be used in the compositions or administered separately, orsupplemental therapy may be included in a course of treatment for apatient. The pharmaceutical compositions may desirably be in the form ofsolutions of suspensions for injection or in forms for topicalapplication including application in for example the oral cavity.Application in other cavities is also possible. Suitable carriers anddiluents are well known in the art and the compositions may includeexcipients and other components to provide easier or more effectiveadministration.

Following administration to the patient, photodynamic therapy may becarried out in a conventional manner, using light sources and deliverysystems that are known in the art, for example, see Phys. Med. biol.(1986), 31, 4, 327-360.

Enhanced positioning of the compounds of formula I in relation totreating tumours may be achieved. For example, the compounds of thepresent invention may be combined with other chemical moieties.

Thus a further aspect embraces compositions comprising such compoundsplus a targeting molecule (e.g. an antibody) which may be part of abinding pair, the other member of the pair being located or concentratedin the target site (e.g. an antigen associated with a tumour). Aparticular compound could be combined, for example, by chemicalattachment, with an antibody tailored to attach itself to the tumoursite. Antibodies as prepared from cultured samples of the tumour.Examples include P.L.A.P. (Placental Alkaline Phosphatase), H.M.F.G.(Human Milk Fat Globulin), C.E.A. (Carcino Embryonic Antibody), H.C.G.(Human Chorionic Gonadotrophin).

Other targeting molecules may include lectins, protein A, nucleic acids(which bind complementary nucleic acids) etc.

Further possible uses of Pcs (as photosensitizers) include use asanti-virals in blood-banks or insecticides.

LCDs

It is well known that some phthalocyanine compounds exhibit liquidcrystalline behaviour.

The majority of known liquid crystalline compounds have a generallyrod-shaped molecular structure and are often characterised by nematicand/or smectic mesophases. There are, however, a number of knowncompounds which are characterised by a generally disc-like molecularstructure. These compounds are termed discotic compounds, which can becharacterised by discotic nematic or columnar mesophase(s).

Discotic compounds can be based on a number of “cores”, e.g. benzene,truxene, metallophthalocyanine, phthalocyanines and triphenylene.

Certain compounds of the present invention e.g. Ni, Cu, Co and 2Hcontaining compounds, have been demonstrated to exhibit columnarmesophases.

Guillon et al Mol. Cryst. Liq. Cryst.; 1985, vol. 130, pp223-229,discuss columnar mesophases from metallated and metal free derivativesof phthalocyanine in which the phthalocyanine is substituted on thebenzene rings with various groups all of which are attached to thephthalocyanine core via a CH₂ unit.

Piechocki and Simon, New Journal of Chemistry, vol. 9, no 3, 1985,pp159-166, report the synthesis of octa-substituted phthalocyaninederivatives forming discotic mesophases. The side chains are linked tothe phthalocyanine core via a CH₂ unit.

Most liquid crystal compounds are known as thermotropic liquid crystalcompounds. Thermotropic liquid crystals exist in dependence of thetemperature in certain temperature intervals. In some cases whendifferent substances are mixed together with a solvent the mixture canexhibit different phases not only as the temperature is changed, butalso as the concentration of the solute is changed. When the liquidcrystal phase is dependent on the concentration of one component inanother it is called a lyotropic liquid crystal. The easiest way to makea lyotropic liquid crystal mixture is to start with a molecule thatpossesses end groups with different properties. For example one endcould show an affinity for water and the other end tends to excludewater. Molecules which possess both a hydrophilic group and a part whichis a hydrophobic group can display characteristics of both classes,therefore they are called amphiphilic molecules.

Lyotropic liquid crystals have numerous potential applications includingdetergents, the recovery of oil from porous rocks and in the foodindustry, providing they are sufficiently non-toxic, for example as foodemulsifiers. There may also be medical applications for lyotropic liquidcrystal systems. For example, amphiphilic materials could help to makedrugs more soluble in the blood.

For a review of phthalocyanine thermotropics, see Simon and Bassoul inPhthalocyanines, Properties and Applications, Ed., C. C. Leznoff and A.B. P. Lever, V. C. H. Publishers 1992, p227.

Liquid Crystal Devices

One aspect of the invention includes use of the compounds of Formula I,and use of mixtures including Formula I, in a liquid crystal device.Typically such devices include linear and non-linear electrical, opticaland electro-optical devices, magneto-optical devices, and devicesproviding responses to stimuli such as temperature changes and total orpartial pressure changes. The devices themselves form a further aspectof the present invention.

A typical example of the use of a compound of Formula I in a liquidcrystal material and device embodying the present invention will now bedescribed with reference to FIG. 4.

The liquid crystal device consists of two transparent plates, 1 and 2,in this case made from glass. These plates are coated on their internalface with transparent conducting electrodes 3 and 4. An alignment layer5, 6 is introduced onto the internal faces of the cell so that a planarorientation of the molecules making up the liquid crystalline materialwill be approximately parallel or at a small angle to the glass plates 1and 2. For some types of display the plane of the molecules isapproximately perpendicular to that of the glass plates, and at eachglass plate the alignment directions are orthogonal. The electrodes 3, 4may be formed into row and column electrodes so that the intersectionsbetween each column and row form an x, y matrix of addressable elementsor pixels. A spacer 7 e.g. of polymethyl methacrylate separates theglass plates 1 and 2 to a suitable distance e.g. 2 microns. Liquidcrystal material 8 is introduced between glass plates 1, 2 by fillingthe space in between them. The spacer 7 is sealed with an adhesive 9 ina vacuum using an existing technique. Polarisers 10, 11 are arranged infront of and behind the cell. For some devices, only one or even nopolarisers are required.

The device may operate in a transmissive or reflective mode. In theformer, light passing through the device, e.g. from a tungsten bulb, isselectively transmitted or blocked to form the desired display. In thereflective mode a mirror (12) is placed behind the second polariser 11to reflect ambient light back through the cell and two polarisers. Bymaking the mirror partly reflecting the device may be operated both in atransmissive and reflective mode.

The alignment layers 5,6 have two functions one to align contactingliquid crystal molecules in a preferred direction and the other to givea tilt to these molecules—a so called surface tilt—of a few degreestypically around 4E or 5E. The alignment 5, 6 may be formed by placing afew drops of the polyimide onto the cell wall and spinning the walluntil a uniform thickness is obtained. The polyimide is then cured byheating to a predetermined temperature for a predetermined time followedby unidirectional rubbing with a roller coated with a nylon cloth.

Laser Addressed Applications

Some phthalocyanines also absorb radiation in the far-red to nearinfra-red regions of the electromagnetic spectrum. Compounds whichabsorb strongly at wavelengths of laser light can in principle beexploited as guest dyes dissolved in liquid crystalline host materialsin a laser addressed system.

Materials have been proposed for laser addressed applications in whichlaser beams are used to scan across the surface of the material or leavea written impression thereon. For various reasons, many of thesematerials have consisted of organic materials which are at leastpartially transparent in the visible region. The technique relies uponlocalised absorption of laser energy which causes localised heating andin turn alters the optical properties of the otherwise transparentmaterial in the region of contact with the laser beam. Thus as the beamtraverses the material, a written impression of its path is left behind.One of the most important of these applications is in laser addressedoptical storage devices, and in laser addressed projection displays inwhich light is directed through a cell containing the material and isprojected onto a screen. Such devices have been described by Khan Appl.Phys. Lett. Vol. 22, p111, 1973; and by Harold and Steele in Proceedingsof Euro display 84, pages 29-31, September 1984, Paris, France, in whichthe material in the device was a smectic liquid crystal material.Devices which use a liquid crystal material as the optical storagemedium are an important class of such devices. The use of semiconductorlasers, especially Ga_(x)Al_(1-x)As lasers where x is from 0 to 1, andis preferably 1, has proven popular in the above applications becausethey can provide laser energy at a range of wavelengths in the nearinfra-red which cannot be seen and thus cannot interfere with the visualdisplay, and yet can provide a useful source of well-defined, intenseheat energy. Gallium arsenide lasers provide laser light at wavelengthsof about 850 nm, and are useful for the above applications. Withincreasing Al content (x<1), the laser wavelength may be reduced down toabout 750 nm.

One of the main problems associated with the use of the above materialsis that it has proved difficult to provide materials which aretransparent in the visible region and yet are strong absorbers in eitherthe UV or IR region, preferably in the near-IR region. The use of dyeswithin these materials can provide strong absorption at certainwavelengths, but few dyes are transparent in the visible region and manyare insoluble in the type of materials used for laser addressedapplications. EP-A-0155780 discloses a group of metal and metal-freephthalocyanines which have been used as infra-red absorbing dyes for anumber of applications. These phthalocyanines contain from 5 to 16peripheral organic substituent groups that are linked to thephthalocyanine through sulphur, selenium, tellurium, nitrogen or oxygenatoms. However, very few of the groups disclosed absorb infra-redradiation strongly at or near the wavelength of a gallium arsenide laser(850 nm). This problem also applies to a further group of infra-redabsorbing phthalocyanines disclosed in EP-A-0134518. This further groupconsists of naphthalocyanines which are peripherally substituted withalkyl groups and centrally substituted with a metal atom or a chloride,bromide or oxide thereof. Materials Science II/1-2, 1976 pp 39-45discloses the synthesis of octamethoxyphthalocyanines but these areinsoluble in organic solvents and as such are unsuitable for acting asdyes in liquid crystalline solvents for laser addressed systems. Variousof the compounds of the present invention are particularly suitable forthis application owing to their high solubility and the retention ofhigh absorbance at appropriate wavelengths even at high concentrations.The absorption maxima may be controlled by altering the central atom, orby use of additives (e.g. metal salts) or other agents to (e.g. pyridineto decomplex ZnAzaPc).

Optical Recording Media

For corresponding reasons to those discussed above, the compounds of thepresent invention will be suitable for use in optical recording media.Typically the phthalocyanine will absorb in the near-infrared. In orderto make an optical recording media using a near-infrared absorber, thenear-infrared absorber may be coated or vacuum-deposited onto atransparent substrate. European patent application EP 0 337 209 A2describes the processes by which the above optical-recording media maybe made. Further the materials described in EP 0 337 209 A2 are usefulin near-infrared absorption filters and liquid crystal display devices,as are the compounds described by the current invention. As described inEP 0 337 209 A2, display materials can be made by mixing a near-infraredabsorber of formula I with liquid crystal materials such as nematicliquid crystals, smectic liquid crystals and cholestric liquid crystals.The compounds of the current invention may be incorporated into liquidcrystal panels wherein the near-infrared absorber is incorporated withthe liquid crystal and laser beam is used to write an image. Mixtures ofphthalocyanines of the current invention may be mixed with liquidcrystal materials in order to be used in guest-host systems. GB2,229,190 B describes the use of phthalocyanines incorporated intoliquid crystal materials and their subsequent use in electro-opticaldevices.

The properties of spin coated films of compounds of the presentinvention are discussed hereinafter. Such spin coated films may beuseful in the production of optical recording media, and also insensors.

Sensors

Films of Pcs of the prior art have been used for as the active componentin conductometric and optical based sensors. They may also have utilityas selective gas sensors (e.g. for N₂), as demonstrated by thealteration in spectral properties which occurs in the presence ofparticular gasses e.g. HCl (see Figures below).

Langmuir-Blodgett (LB) Films

The materials of the current invention may also be incorporated inLangmuir-Blodgett (LB) films. LB films incorporating phthalocyanines ofthe current invention may be laid down by conventional and well knowntechniques, see R. H. Tredgold in ‘Order in Thin Organic Films’,Cambridge University Press, p74, 1994 and references therein. Generallyan LB film is prepared by depositing a monolayer of a surface-activematerial onto a water surface; this may be done using well establishedtechniques. The molecules of the surface active material align in themonolayer, the hydrophilic ends remaining in the water, and thehydrophobic end projecting out of the surface. By other known techniquesthis monolayer may be transferred essentially intact onto the surface ofa solid substrate and further monolayers deposited on the layer on thesubstrate to form a film, i.e. an LB film.

LB films including compounds of the current invention may be used asoptical or thermally addressable storage media.

Molecular Wires

The compounds of the current invention may also be used as molecularwires, see R. J. M. Nolte et al, Angew, Chem. Int. Ed. Eng., vol. 33,part 21, page 2173, 1994.

Photonic Devices

It is known that some phthalocyanines are excellent generators of thirdorder non-linear optical effects and thus show promise for use inphotonic devices including all-optical switches and computers, seeBredas, Adant, Tackx Persoons and Pierce, Chem. Rev., 94, p243, 1994.The materials of the present invention may show such effects and be usedin such devices. In particular the distortion of the delocalised Bsystem of the AzaPc which may be induced by the pyridine ring may beexpected to produce novel properties as compared with prior art PCs usedfor this purpose.

Redox Applications

The compounds of the present invention allow for electronic interactionof substituents with the Azaphthalocyanine ring. The redox properties ofthe Azaphthalocyanines described by the current invention may be easilymodified by the altering the identity of the various substituents. Thecompounds described by the current invention are therefore useful in anyone or more of the following: electrocatalysis, photocatalysis,photovoltaics (e.g. solar cells), electric conduction, photoconductivityand electrochromism and other applications which exploit redoxproperties.

Polyelectrolytes

Polyethylene oxides can complex alkali metal ions, for example Li+ andhave been used as polyelectrolytes in solid state battery applications,see Charadame in ‘Macromolecules’, ed. Benoit and Rempp, Pergamon press,New York, 1982, p226. The compounds of the invention may also be usefulas polyelectrolytes, they are able to stabilise charge, therefore thereexist a number of applications within battery technology.

Further aspects of the invention:

As well as use in the methods described above, in a further aspect ofthe invention there is a disclosed a method of preparing the compoundsof the present invention, substantially as described hereinafter.

Dimers or higher oligomers comprising or consisting of the compounds ofthe present invention are also embraced within its scope. Particularlyembraced are “edge-to-face” dimers, including mixed dimers formedbetween one compound of the present invention and another Pc or AzaPc.

It may be advantageous to polymerise certain of the compounds describedby the current invention. Polymerised phthalocyanines may be used in,for example, LB films. There are numerous ways by which thephthalocyanine compound may be polymerised. Polymerisation may beeffected via one or more of the positions R_(n) or R_(p) as described informula I of the current invention or via the central metal atom ormetal compound, or polymerisation may be realised by a combination ofthe above methods. An example of a suitable phthalocyanine substituentwhich may be used to effect polymerisation is an unsaturated substituentsuch as an alkene group.

Main chain or side chain liquid crystal polymers may also be made usingthe compounds of the present invention, or metal-linked liquid crystalpolymers.

FIGURES

FIG. 1(a) shows Pc

FIG. 1(b) shows Formula I

FIG. 1(c) shows Formula II

FIG. 1(d) shows Formula III

FIG. 1(e) shows Formula IV

FIG. 1(f) shows Formula V

FIG. 1(g) shows Formula VI

FIG. 1(h) shows:

Top. 250-800 nm spectrum of 1 a as a solution in cyclohexane at1.46×10⁻⁶M; λ_(max) 710 nm (ε1.36×10⁵), 687 nm (ε0.95×10⁵). Insetspectrum (scale not shown) shows the Q-band absorption at 1.46×10⁻⁴M;λ_(max) 709 nm (ε6.23×10⁴), 687 nm (ε5.85×10⁴), 652 nm (ε4.33×10⁴).

Middle, as above but for 1 b at 1.04×10⁻⁶M; λ_(max) 694 nm (ε1.16×10⁵),679 nm (ε1.17×10⁵). Inset spectrum, Q-band absorption at 1.04×10⁻⁴M;λ_(max) 690 nm (ε5.61×10⁴), 679 nm (ε6.15×10⁴), 643 nm (68 4.27×10⁴).

Bottom, as above but for 1 c at 1.24×10⁻⁶M; λ_(max) 716 nm (ε0.86×10⁵).Inset spectrum, Q-band absorption at 1.24×10⁻⁴M; λ_(max) 715 nm(1.25×10⁵), 679 mn (ε0.75×10⁵).

FIG. 2

Transmission electron micrograph of 1 b as a THF gel on a carbon coatedcopper grid. The field of view is 453×294 nm.

FIG. 3

The visible region spectra of spin coated films of 1 a (FIG. 3a), 1 b(FIG. 3b) and 1 c (FIG. 3c). FIG. 3d shows the film of 1 c afterexposure of Hcl vapour. Within 30 days after exposure to HCl, the filmgives a spectrum the same as that in FIG. 3c.

FIG. 4

A liquid crystal device as described in Example 4.

FIG. 5

Some of the compounds of the present invention which were produced asdescribed in Example 1.

FIG. 6

A putative mixed (“edge to face”) dimer complex of the presentinvention.

FIG. 7

Scheme 1, showing phase transitions determined by DSC and opticalmicroscopy. Enthalpy data were determined by DSC at a heating/coolingrate of 10° C. min⁻¹ K and K₁ refer to crystal phases. The highertemperature mesophase for 1 a and 1 b appears as a fan texture whenviewed through a polarised light microscope, characteristic of acolumnar mesophase with hexagonal cross sectional symmetry in which thecolumns are disordered; ie D₂. The lower temperature mesophase shows aneedle type texture comparable with that assigned elsewhere to a secondD₁ mesophase within the octaalkylphthalocyanine series.

EXAMPLES Example 1

Preparation of Compounds of the Present Invention

Briefly, the novel macrocyclic derivative Formula VI, wherein M was 2H(designated 1 a) was obtained by reaction of 3,4-dicyanopyridine withexcess 3,6-dioctylphthalonitrile⁹ under basic (lithium pentyloxide)conditions. Following conventional workup, 1 a (10%) was separatedchromatographically from the principal by-product,1,4,8,11,15,18,22,25-octaoctylphthalocyanine.⁹

The compounds 81 to 88 shown in FIG. 5 were generated from themetal-free compound 80 (=1a) as exemplified by the Cu, Zn and Niderivatives described below.

Preparation of1,4,8,11,15,18-(hexaoctyl)tribenzo-3,4-pyridinoporphyrazine

In a typical procedure, 3,6-dioctylphthalonitrile (3.17 g, 9 mmol) and3,4-dicyanopyridine (0.13 g, 1 mmol) in dry pentan-1-ol (30 ml) wereheated under reflux with stirring and lithium metal (0.2 g) was addedslowly in small portions. The solution turned an intense green colourimmediately and reflux was continued for 6 hours, then the mixture wasallowed to cool to room temperature and glacial acetic acid (50 ml) wasadded and stirring continued for 30 minutes. The solvents were removedunder reduced pressure and the mixture washed onto a filter withmethanol (500 ml) to remove non-phthalocyanine impurities, the rest ofwhich were left on the filter when the Pcs were taken up in THF. Thesolvent was removed under reduced pressure and the mixture was separatedusing column chromatography over silica gel. The first green fractioncontained only metal-free 1,4,8,11,15,18,22,25-octaoctylphthalocyanineusing as eluent light petroleum. The next green fraction was collected,eluent THF, and further purified by column chromatography over silicagel, eluent cyclohexane-THF (9:1) and recrystallised from THF-methanolto afford 1,4,8,11,15,18-(hexaoctyl)tribenzo-3,4-pyridinoporphyrazine asa blue solid (125 mg, 10% based on 3,4-dicyanopyridine). Mp 142° C.(K-D), 242EC (D-I); FAB-MS (LSIMS) m/z 1188. (Found: C, 79.54; H, 9.55;n, 10.65. C₇₉H₁₁₃N₉ requires: C, 79.82; H, 9.58; n 10.60). ν_(max)(DCM)/cm⁻¹: 3285 (NH) and 1600 (aromatic); δ_(H) (270 MHZ; C₆D₆): −2.17(br s, 2H), 0.85-0.96 (m, 18H), 1.20-1.95 (m, 60H), 2.2-2.5 (m, 12H),4.10 (br s, 4H), 4.43 (M 4H), 4.54 (m, 4H), 7.65-7.8 (m, 4H), 7.86 (s,2H), 8.53 (d, 1H), 9.14 (d, 1H), 10.35 (s, 1H); λ_(max)(cyclohexane)/nm: 328, 687 and 710. The third fraction to be collectedwas obtained using cyclohexane-THF (2:1) as eluent and recrystallisedfrom THF-methanol to afforddi-3,4-pyridino-1,4,8,11-(tetraoctyl)dibenzo-porphyrazine as a dark bluesolid (5 mg, 1% based on 3,4-dicyanopyradine). Mp 250EC (K-D), 326(D-I); FAB (LSIMS) m/z 966; (Found: C, 77.25; H, 8.53; N, 14.24C₆₂H₈₀N₁₀ requires: C, 77.14; H, 8.35; N,14.51). δ_(H) (270 MHZ; C₆D₆;50EC): −4.35-−3.83 (t, 2H), 0.95 (t, 12H), 2.15-2.41 (m, 8H), 3.94 (m,4H), 4.20 (m, 4H), 7.59-7.74 (m, 4H), 8.19-8.30 (m, 2H), 8.96-9.03 (m,2H), 10.04-10.15 (t, 2H). δ_(max) (cyclohexane)/nm: 324, 669, 705.

Preparation of Copper1,4,8,11,15,18-(hexaoctyl)tribenzo-3,4-pyridinoporphyrazine

In a typical procedure, copper(II) acetate (0.2 g) was added to astirred solution of1,4,8,11,15,18-(hexahexyl)tribenzo-3,4-pyridinoporphyrazine (70 mg) inpentan-1-ol (20 ml) and heated under reflux for 90 minutes. The solventwas removed under reduced pressure and the residue purified using columnchromatography over silica gel using as eluent cyclohexane-THF (5:1) andrecrystallised from THF-methanol to afford copper1,4,8,11,15,18-(hexaoctyl)tribenzo-3,4-pyridinoporphyrazine as a bluesolid (48 mg, 65%). Mp 134° C. (K-D), 319° C. (D-I); FAB (LSIMS) m/z1249; (Found: C, 75.84: H, 9.00; N, 9.90. C₇₉H₁₁₁N₉Cu requires: C,75.89; H, 8.95; N, 10.08). λ_(max) (cyclohexane)/nm: 325, 343 629, 649,686, 701.

Preparation of Nickel and Zinc Derivatives

The Ni derivative (designated 1 b) or Zn derivative (designated 1 c)were produced by reactions of 1 a with nickel acetate and zinc acetatein refluxing pentanol generated 1 b (53%) and 1 c (78%). Each gave asatisfactory elemental analysis and low resolution FAB-ms as follows:Found: C, 79.54; H, 9.55, N, 10.65; C₇₉H₁₁₃N₉ requires: C, 79.82; H,9.58; N, 10.60. 1 b, Found: C, 76.10; H, 9.00; N, 9.95; C₇₉H₁₁₁N₉Nirequires: C, 76.18; H, 8.98; N, 10.12. 1 c, Found: C, 75.68; H, 8.78; N,9.95; C₇₉H₁₁₁N₉Zn requires: C, 75.78; H, 8.94; N, 10.07.

All three compounds (1 a, 1 b, 1 c) showed good solubility in solventssuch as THF, toluene, cyclohexane and dichloromethane.

Compounds of the present invention based on a napthalocyanine structure(i.e. azanapthalocyanines) can be prepared by methods analogous to thosedescribed above, in conjunction with the disclosure of Cammidge et al(1997) J Porphyrins Pthalocyanines 1:77-86.

Example 2

Spectra of the Compounds

The properties of the substituted pyridino[3,4]-tribenzoporphyrazines,1, prove to be highly dependent upon the atom(s) at the centre of themacrocycle and reflect the individual compound's propensity for formingeither Face-to-Face assemblies or Edge-to-Edge complexes. The Q-bandabsorptions in the visible region spectra of solutions of 1 a (2H) and 1b (Ni) in cyclohexane at ca. 1×10⁻⁶M are shown in FIG. 1. The twocomponent Q-band of 1 a, top spectrum in FIG. 1, is similar to that of ametal-free Pc. The Q-band of 1 b, the middle spectrum, is also splitλ_(mas) 694 and 679 nm, differing from that of simple metallated Pcs butconsistent with the lower symmetry of the system.¹⁰ Otherwise, the highextinction coefficients of the Q-bands, see legend to FIG. 1, and thevery low intensity absorptions to the blue are characteristic of Pccompounds which are essentially non aggregated. At high concentrations,however, Face-to-Face type aggregation becomes apparent, manifested bythe characteristic enhanced absorption in the region 600 to 690 nm (seethe inset spectra in FIG. 1) and the lower extinction coefficients ofthe lowest energy bands.

The zinc derivative, 1 c, shows different behaviour. The spectrum of 1 cin cyclohexane, the bottom spectrum in FIG. 1, and in dichloromethaneshows enhanced separation of the main Q-band components, λ_(max) 716 and675 nm, within a band envelope which is essentially invariant over theconcentration range ca. 1×10⁻⁷M. In particular, extinction coefficientsremain high at the higher concentrations. Absence of Face-to-Faceaggregation is signified by the lack of significant absorption in thevisible region to the blue of these main bands. The gel permeationchromatogram obtained for elution of 1 c as a solution indichloromethane through PLgel 100A and 500A, 30 cm, 5 micron columns andcalibrated against polystyrene gives a peak molecular mass, Mp, of 2050(M_(w) 1630 and M_(n) 1390). Elution of three model phthalocyaninederivatives under the same conditions showed that the “polystyreneequivalent” molecular masses for these macrocycles are consistently20-25% lower than the actual molecular mass. Thus the Mp obtained for 1c suggests that under the conditions of the GPC experiment, the materialhas formed a dimeric complex.

Thus we assign the visible region spectrum of 1 c, above, to a dimericspecies (or lower oligomeric species) arising from intermolecular axialligation of a pyridyl nitrogen of one macrocycle with the zinc atom of asecond, to form an Edge-to-Face complex. In support of this, we notethat addition of pyridine or THF changes the band shape to one closelyresembling that of non-aggregated 1 b; this we attribute to disruptionof the homoligated complex of 1 c. Similarly, excitation of 1 c (λ_(ex)650 nm) as a solution in toluene at 1.2-10⁻⁵M shows fluorescenceemission at λ_(max) 731 nm. Addition of 100 Fl pyridine raises theemission intensity by a factor of two and shifts the emission band to720 nm. In contrast 1 a under the same conditions shows λ_(em−)721 nm,essentially unchanged when pyridine is added.

Further confirmation of the formation of Edge-to-Face complexes by 1 cwas obtained by ¹H-NMR spectroscopy. The spectrum of 1 c in benzene-d₆shows no signals downfield of δ8.32. Upon addition of pyridine-d₅, thespectrum simplifies and is very similar to that of 1 a. In particular,the pyridyl protons of 1 c now appear at 9.25, 9.43 and 11.12 ppm. Webelieve it likely that higher oligomers may be present at the highersolution concentrations used in the NMR experiment. NMR spectroscopy of1 a (Ni derivative) at 1 mM suggests some degree of edge-to-facestructure, in addition to UV-VIS evidence suggesting face-to-facestructures which is discussed above.

Example 3

TEM

Transmission electron microscopy highlighted differences in packing inthe condensed states of 1 a, 1 b, and 1 c. A drop of a solution of eachcompound in THF (2 mg per ml) was administered onto a copper grid,blotted dry, and viewed through a JEOL 100CX Electron Microscope as thesolvent evaporated. FIG. 2 shows the micrograph obtained for 1 b. Itclearly shows the generation of a columnar structure, formally analogousto the “molecular wires” observed by Nolte et al.¹¹ for a more complexPc derivative. Compound 1 a showed similar behaviour. The width of theassembly depicted in FIG. 2 is ca. 15 times the approximate diameter ofthe individual molecules of 1 b. In contrast, 1 c forms a distinctlydifferent structure, the micrograph showing an apparently featurelessfilm with no evidence of column formation.

Example 4

LC Properties

The differences in the molecular packings in the condensed phase lead todifferent behaviour on heating and cooling. Thus, compounds 1 a and 1 bexhibit thermotropic columnar mesophases; polarised light microscopeshows a fan type structure on cooling from the isotropic liquidconsistent with the hexagonal columnar mesophase exhibited by othernon-peripherally alkyl-substituted Pcs.¹² Phase transition data arereported in Scheme 1 (FIG. 7). In contrast, 1 c does not exhibit amesophase during either heating of the solid sample or upon cooling fromthe liquid phase; this we attribute to the orthogonal packing ofadjacent molecules in the solid state and, presumably, in the liquidstate just prior to crystallisation.

Example 5

Spin Coated Films

Large area evaporated films were formulated by the spin coatingtechnique by administering a drop of solution of each compound in THF(ca. 2 mg in 0.5 ml) onto a glass slide rotating a 2000 rpm. Films soformed were transparent and showed no crystallites when viewed under anoptical microscope. Their visible region spectra are shown in FIG. 3a-3c. Those for the films of 1 a and 1 b are closely similar to the spectraof films of metal-free and nickel1,4,8,11,15,18,22,25-octa-octylphthalocyanines respectively^([12])whereas the film spectrum for 1 c, FIG. 3c, is similar to its solutionphase spectrum, albeit blue-shifted by ca. 10 nm. Exposure of the latterfilm to pyridine vapour did not change the spectrum. However, theassembly became disrupted upon exposure to HCl vapour. The new spectrumis shown in FIG. 3d. Within 30 days the original spectrum was recovered,implying that the response to HCl is fully reversible and the moleculesreassemble to give the intermolecular complex.

In conclusion, we have identified a phthalocyanine type macrocycle whosemolecular packing is governed by the central metal ion. BothFace-to-Face and Edge-to-Face packing has been identified. The latter ispromoted by the propensity for zinc to undergo strong axial ligation andcolumnar liquid crystal behaviour, otherwise inherent within the series,is inhibited. Nickel complexes may also undergo weak axial ligation.However, 1 b at UV/vis concentrations and in the liquid crystal phasesfavours Face-to-Face structures in which the Ni(II) d⁸ ion is presumablyin its favoured spin paired, square-planar four coordinate state.

Example 6

An LCD Device

An example of the use of a compound of Formula I in a liquid crystalmaterial and device embodying the present invention will now bedescribed with reference to FIG. 4.

The liquid crystal device consists of two transparent plates, 1 and 2,in this case made from glass. These plates are coated on their internalface with transparent conducting electrodes 3 and 4. An alignment layer5, 6 is introduced onto the internal faces of the cell so that a planarorientation of the molecules making up the liquid crystalline materialwill be approximately parallel or at a small angle to the glass plates 1and 2. For some types of display the plane of the molecules isapproximately perpendicular to that of the glass plates, and at eachglass plate the alignment directions are orthogonal. The electrodes 3, 4may be formed into row and column electrodes so that the intersectionsbetween each column and row form an x, y matrix of addressable elementsor pixels. A spacer 7 e.g. of polymethyl methacrylate separates theglass plates 1 and 2 to a suitable distance e.g. 2 microns. Liquidcrystal material 8 is introduced between glass plates 1, 2 by fillingthe space in between them. The spacer 7 is sealed with an adhesive 9 ina vacuum using an existing technique. Polarisers 10, 11 are arranged infront of and behind the cell. For some devices, only one or even nopolarisers are required.

The device may operate in a transmissive or reflective mode. In theformer, light passing through the device, e.g. from a tungsten bulb, isselectively transmitted or blocked to form the desired display. In thereflective mode a mirror (12) is placed behind the second polariser 11to reflect ambient light back through the cell and two polarisers. Bymaking the mirror partly reflecting the device may be operated both in atransmissive and reflective mode.

The alignment 5, 6 have two functions one to align contacting liquidcrystal molecules in a preferred direction and the other to give a tiltto these molecules—a so called a surface tilt—of a few degrees typicallyaround 4 or 5°. The alignment 5, 6 may be formed by placing a few dropsof the polyimide onto the cell wall and spinning the wall until auniform thickness is obtained. The polyimide is then cured by heating toa predetermined temperature for a predetermined time followed byunidirectional rubbing with a roller coated with a nylon cloth.

Example 7

Gas Sensor

In another example a layer of liquid crystal material is exposed to agas to provide a gas sensor.

Example 8

Mixed Dimers

Upon introduction of 1.0 eq of Zn1,4,8,11,15,18,22,25-octahexylphthalocyanine (designated 6Zn in FIG. 6)into the ¹H NMR solution of compound 80 in C₆D₆ there was no signalobserved downfield of δ8.05. Prior to this addition the signals for thepyridyl protons appeared 8.53, 9.14, 10.35 ppm. Instead of three signalsrepresenting the methylene protons next to the ring, four signalsappear. This seems to suggest that on formation of a dimeric complexthrough the coordination of the pyridine unit of compound 80 to the zinccentre of the 6Zn; the ring current of the 6Zn shields two methyleneprotons of 80 to a significant degree causing an upfield shift of 0.43ppm. The N-H proton of 80 is shifted downfield by 0.55 ppm.

REFERENCES

1. Phthalocyanines—Properties and Applications, eds. Leznoff and Lever,VCH Publishers, New York, 1989.

2. Cook, in Spectroscopy of New Materials, eds. Clark and Hester, Wiley,Chichester, 1993,p.87.

3. Simon and Bassoul, in Phthalocyanines—Properties and Applications,eds. Leznoff and Lever, VCH Publishers, New York, 1993, vol.2,p.223.

4. See, for example, Mason et al. J.Chem.Soc., Dalton Trans. 1979,676.

5. Pomogailo and Wöhrle, in Macromolecule-Metal Complexes, eds.Ciardelli et al. Springer, Berlin-Heidleberg, 1996, p.11; Hanack andLang, Adv. Mater, 1994,6,819.

6. Eg. Shachter et al., J.C.S.Chem.Commun. 1988, 960; Fleischer andShachter, Inorg.Chem., 1991,30,3763;Hunter and Sarson,J.C.S.Chem.Commun., 1994,33,2313; Funatsu et al., Chem.,Lett., 1995,765;Anderson et al., Angew.Chem.Int.Ed.Engl., 1995,34,1096; Alessio et al.,J.C.S.Chem.Commun., 1996,1411-1412.

7. Linstead et al., J.Chem.Soc., 1937,911.

8. Yokote and Shibamiya. Kogyo Kagaku Zasshi, 1959,62,224. Chem.Abs.1961,24019; Yokote el al., Kogyo Kagaku Zasshi, 1964, 67, 166. Chem.Abs.61, 3235; Yokote et al.. Yuki-Gosei Kagaka Kyokaishi 1965,23,151.Chem.Abs. 71,38931h; Sakamoto and Shibamiya, J.Japn.Soc.Colour Material,1985,58,121; Sakamoto and Shibamiya, J.Japn.Soc.Colour Material,1986,59,517.

9. Chambrier et al., J.Mater.Chem., 1993,3,841.

10. cf. Kobayashi et al., J.Am.Chem.Soc., 1996,118,1073; Cook andJafari-Fini, J.Mater.Chem., 1997,7,5.

11. van Nostrum et al., Angew.Chem., Int.Ed.Engl., 1994,33,2173; vanNostrum et al., J.Am.Chem.Soc., 1995,117,9957.

12. Cherodian et al., Mol.Cryst.Liq.Cryst., 1991,196,103.

What is claimed is:
 1. A compound having formula V;

wherein M is selected from: a metal atom; a metal compound; 2H wherebyone H is bonded to each of the two nitrogen atoms depicted as beingbonded to M (positions 29 and 31 shown) R₁, R₃, R₄, R₉, R₁₀, R₁₆, R₁₇,R₂₃, and R₂₄ are H; R₈, R₁₁, R₁₅, R₁₈, R₂₂, and R₂₅ are the same ordifferent and are independently selected from: C₁ to C₃₂ alkyl; C₂ toC₃₂ alkenyl; X—O—Y; X—phenyl, X²COOX¹, X²CONR¹R¹¹, H; halide; wherein: Xand X² are independently selected from: a chemical bond,—(CH₂)_(n)—wherein n is an integer from 1 to 32,—(CH₂)_(a)—CH═CH(CH₂)_(b) where a and b are independently selected fromintegers 0-32 and a+b totals 32; X¹ and Y are independently selectedfrom: C₁ to C₃₂ alkyl, C₂ to C₃₂ alkenyl, and H; R¹ and R¹¹ areindependently selected from: H; C₁ to C₃₂ alkyl, and C₂ to C₃₂ alkenyl,with the proviso that at least one of R₈, R₁₁, R₁₅, R₁₈, R₂₂, and R₂₅ isselected from: C₁ to C₃₂ alkyl, C₂ to C₃₂ alkenyl, X—O—Y, X—phenyl,X²COOX¹, X²CONR¹R¹¹.
 2. A compound as claimed in claim 1 wherein allnon-peripheral R groups other than those attached to pyridyl nuclei areselected from: alkyl containing up to 32; up to 20; between 4-14; orbetween 8-12 C atoms where one or more adjacent CH₂ groups may bereplaced by O or a double bond, and the remaining R groups are all H. 3.A compound as claimed in claim 1 wherein alkyl groups present within theR groups are straight chain alkyl.
 4. A compound as claimed in claim 1wherein M is selected from: 2H; Ru, Ni, Pb, V, Pd, Co, Nb, Al, Sn, Zn,Cu, Mg, Ca, In, Ga, Fe, Eu, Lu and Ge.
 5. A compound as claimed in claim4 wherein M is selected from: 2H; Zn; Cu; Co; Ru; and Ni.
 6. A compoundas claimed in claim 5 having formula VI

wherein M in selected from: 2H; Zn; Ni.
 7. A compound as claimed inclaim 1 which has an absorption maximum in the near infra-red.
 8. Acomposition comprising a compound as claimed in claim 1 in a carrier. 9.A pharmaceutical composition comprising a compound of claim 1 inadmixture with a pharmaceutically acceptable carrier.
 10. Apharmaceutical composition as claimed in claim 9 which is in the form ofsolution suitable for injection into a patient.
 11. A dimer consistingof a compound as claimed in claim 1.